Last updated on December 4th, 2025 at 12:06 am
The Powertrain Control Module, or PCM, is a pre-programmed digital computer that operates the engine control system of a vehicle. People refer to it as JTEC sometimes. As the input data changes, the PCM adjusts its response to the various output devices it operates. If the PCM, the “brains”, fails to work correctly, the rest of the engine will have issues as well. Luckily, if proper diagnosis points toward replacement of the PCM as the solution, the PCM can be easily replaced to fix the issue. We’ll show you how to replace a PCM ECM ECU Module on a 1999 Jeep Grand Cherokee.
Begin replacing the PCM of your 1999 Jeep Grand Cherokee by locating the module. A TCM, Transmission Control Module, might be equipped in that area and will need to be removed to replace the PCM. The coolant reserve/overflow tank will be in the way but the location of the PCM is on the cowl panel in the right/rear side of the engine compartment.
REMOVAL
1- Disconnect negative battery cable from the battery.
2- If equipped, remove the Transmission Control Module (TCM).
3- Remove the coolant reserve/overflow tank.
4- Remove cover over the electrical connectors. Cover snaps onto the PCM.
5- Carefully unplug the three 32–way connectors from the PCM.
6- Remove the three PCM bracket-to-body mounting nuts.
7- Remove the PCM/PCM bracket assembly itself from the vehicle.
8- Remove the 3 PCM-to-PCM bracket bolts (screws).
REPLACEMENT
1- Check for damaged pins in the three 32–way electrical connectors. If pins not damaged, continue.
2- Install PCM to its mounting bracket. Tighten the three mounting bolts to 3 N·m (25 in. lbs.) torque.
3- Install PCM/PCM bracket to the body. Install the 3 nuts and tighten to 9 N·m (80 in. lbs.) torque.
4- Install the three 32–way connectors.
5- Install cover over the electrical connectors. Cover snaps onto the PCM.
6- Install the coolant reserve/overflow tank.
7- Reinstall the Transmission Control Module (TCM), if needed.
8- Reconnect the negative battery cable back to the battery.
We have a huge selection of Programmed 1999 Jeep Grand Cherokee PCMs if a replacement PCM is needed. The PCM you order with us is 100% ready for immediate installation. If you have any questions, please don’t hesitate to call our Customer Service department at 516-766-2223, we’re always here to help!
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